The present technology relates to semiconductors and/or non-volatile memory devices.
Most semiconductor devices include an input circuit configured to receive signals from the outside world via input pads (or pins) and an output circuit configured to provide internal signals to the outside via output pads (or pins). The input circuit has a termination resistor for impedance matching of the external transmission line. The output circuit has an output driver, which has a resistance (Ron). The impedance of both the termination resistor and the output driver can change due to various circumstances such as variation of a power supply voltage, a change in operating temperature, etc. Thus, an impedance mismatch can arise.
The impedance mismatch can cause signal reflection, which can compromise signal integrity. As the operating speed of electrical products has increased, the swing width (that is the difference between high and low logic levels) of a signal interfaced between semiconductor devices gradually has been reduced in order to minimize a delay time taken for signal transmission. However, the reduction in the swing width of the signal easily exposes the signal to external noise, causing signal reflection to become more critical at an interface terminal due to impedance mismatch. Thus, the impedance mismatch may lead to a difficulty in high-speed transmission of data and distortion of output data.
To alleviate impedance mismatch, the device's output drivers and the device's termination resistor are periodically calibrated. For example, just after the device is reset, a ZQ calibration command may be sent to the device. This is referred to as a long ZQ calibration command. After the initial calibration has been performed, a short ZQ calibration command may be sent to the device to update the calibration. Typically, the device is not given as long to complete the short ZQ calibration command, as it is to complete the long ZQ calibration command. It can be challenging for the device to be able to complete the short ZQ calibration command within the time limit.